Numerous reports have been published to date on transition metal complex catalysts usable in catalytic asymmetric syntheses such as asymmetric hydrogenation reactions, asymmetric hydrosilylation reactions, asymmetric hydroformylation reactions and asymmetric isomerization reactions. Among these, transition metal complexes of ruthenium, iridium, rhodium, palladium, nickel or the like, which contain optically active phosphines as ligands, have been reported to possess excellent performance as catalysts for asymmetric synthetic reactions, and some of them are already used in the industrial application [Asymmetric Catalysis in Organic Synthesis, Ed., R. Noyori, Wiley & Sons (1994)].
Phosphole compounds, meanwhile, have been extensively studied for many years with respect to their syntheses and physical properties, but there are still few instances confirming the fact that phosphole compounds were applied to syntheses or asymmetric reactions of optically active substances.
In recent years, some optically active diphosphine ligands each containing one or more phosphole moieties have been reported, and have also been applied to asymmetric hydrogenation reactions (J. Mol. Cat., 72, 21–25, 1992; Organometallics, 20, 1014–1019, 2001).
Among the compounds reported so far are chiral transition metal complexes of chiral bis(phosphorane) obtained using chiral 1,4-diol cyclic sulfate esters as precursors (JP 6-508848 A), diphosphine derivatives (JP 7-149777 A), diphosphole derivatives (JP 2002-527444 A), isophosphindolinic acids (JP 2002-527445 A), etc.
However, these optically active diphosphine ligands, each of which contains one or more phosphole moieties, are not yet free from the problems associated with the industrial viewpoint, because their syntheses are all required to go through cleavage by metallic lithium of carbon-phosphorus bonds in the corresponding 1-phenylphosphole compounds.
Moreover, these ligands require improvements of catalysts if they are not sufficient in selectivity (chemical selectively, enantio-selectivity) and catalytic activities, depending on this reaction targets or their reaction substrates.